[tommage1]

Have a nearly full 4TB backup drive for one of my Roamios (you can have multiple drives for Roamios if on same OS but that is not the point of this thread). Anyway I want to use the 4TB for a different project. And I have a couple Seagate 2.5" 4TB SMR drives I bought as possible Bolt upgrade drives back in the day before most people knew the difference between CMR and SMR and that SMR is not good for Tivos.

So I decided to clone the nearly full 3.5 CMR 4TB to one of the Seagate 2.5 SMR 4 TB. I tried a cloning dock first, one I use for cloning all the time. It seems to start, but after 6 or so hours the 25% light was still flashing, that is what shows when it starts. Tried it one more time, same result. So decided to try an MFST copy. That did work. My gosh it was slow, took almost 33 hours. Speed showed like 30 MB/s direct motherboard type Sata connections. Normally when doing an MFST copy I get 80 MB/s I believe. So must be slower because copying to an SMR drive? I put the 2.5 copy into the Roamio. It booted up fine. Could see all the recordings. However navigating menus very slow, lot of blue spinning circles. Got error when trying to play some recordings. When I tried connecting to Tivo it got to "loading" but failed. So rebooted. VERY slow, though it finally made it. Same problems though. So ran a kickstart 58 on it. Seemed to have worked. Can watch the recordings that had an error before. And connected successfully to Tivo.

Guess I will set aside the 2.5 SMR drive as my backup. I would never actually use an SMR drive in a Tivo if I have a choice (which you always do, with Bolts and Edge can just use external 3.5 CMR). Not 100% sure the copy is fully functional but will take a chance. If/when I want to use it I would clone back to a CMR 3.5, just nice to find a use for one of the SMR 2.5s that was sitting around gathering dust. And free up a 4TB CMR 3.5. An interesting project regardless, I enjoy playing around with Tivos.

 

[Worf]

SMR drives are slower for sustained writes. They have a CMR landing zone which buffers writes initially. This makes initial writes very fast as it's CMR recorded. After around 20GB or so the area fills up and the drive is forced to clean the area out. For SMR drives, writing a sector requires rewriting the entire zone, so the drive will copy the zone to a new spot on the disk for temporary holding, then write the zone back with the modified sectors on it, which frees up space in the CMR landing area for new data.

In more typical desktop operations, writes happen to the CMR area, and the instant the drive goes idle, it starts clearing the CMR area and rewriting the zones in the background while it's not busy so to keep the CMR area clear. With the right usage pattern, the drive never slows down.

However, applications that are constantly writing to it mean the drive cannot find time to clear out the CMR area and it's forced to do it on the fly - if it's full, the disk has to make space by moving data from the CMR to the SMR section then accepting data into the CMR area.

This means while the drive can easily get 100+MB to the media on CMR, it will significantly slow down to around 30MB/sec or less when it has to clean up during a write by moving the data to the SMR area.

SMR is perfectly acceptable for light desktop use, or for archival storage where data is rarely overwritten - you often store new data but rarely overwrite existing data.

 

[tommage1]

This means while the drive can easily get 100+MB to the media on CMR, it will significantly slow down to around 30MB/sec or less when it has to clean up during a write by moving the data to the SMR area.

That definitely explains the 30 MB/s speed I got during the MFST copy, almost exact the entire 33 hours. I wonder if it is limited to 30MB/s or so in a cloning dock also. That would explain why even after 6 hours in a dock it had not moved off the 25% line, maybe it needed 8 hours plus. Normally when doing CMR to CMR clone the dock would be twice as fast as even motherboard Sata to Sata clone. Perhaps not true when an SMR drive in play, maybe the 30 is the limit even in a cloning dock?

 

[Worf]

The 30MB/sec would be the fastest the drive could currently accept data when the landing zone is full. With a CMR drive, they can do media speeds of 120+MB/sec, and an SMR drive with an empty landing zone can do this until the landing zone fills up. If that's the case, the drive will have to empty the landing zone in order to make space to land new data, which requires the drive to have to rewrite an entire SMR zone area and update the sectors that the landing zone is temporarily holding.

So it wouldn't matter if you used a PC or a dock - the drive is basically limiting the speed because it's busy.

It does beg the question on whether an SMR aware cloning tool can make copying faster by dumping data to the disk until the landing area is full, then waiting for it to move the data off, then filling it up again.

 

[tommage1]

All very interesting (though I rarely use SMR drives for anything). I have no idea if there exists a cloning dock that is SMR aware, probably not. Maybe some sort of tool/software if the clone is being done in a computer. I may experiment one more time, try the CMR to SMR clone in the dock, sounds like it should take almost exactly how long it took in the computer. With both drives hooked up to Sata ports on the board. Since the clone/copy took about 33 hours in the computer the 25% light on the dock should turn solid a bit after 8 hours. I stopped it after 6 hours since I thought it was not working.

I suppose there is a possibility that a cloning dock cannot even handle a CMR to SMR clone. For mine I guess the only way to find out is try it again. Just hope it does not burn out the dock, maybe give it 10 hours and if 25% is not solid turn it off. Or test with smaller drives, however the 4TB SMR drive is the only SMR drive I have available for testing.